There is great interest in producing surfaces whose wettability can be controlled. The ability to control the wettability of a surface allows one to change the extent to which a fluid wets the surface or is repelled from the surface. Moreover, it would be advantageous to dynamically control the wettability of a surface based upon changes in the environment that the surface is exposed to. It would also be advantageous if such changes could be made with a minimum of energy expenditure. Unfortunately, existing surfaces do not provide the desired control of wettability.
For instance, certain surfaces with raised features, such as posts or pins, may provide a superhydrophobics surface. That is, a droplet of liquid on a superhydrophobic surface will appear as a suspended drop having a contact angle of at least about 140 degrees. Applying a voltage between the surface and the droplet can cause the surface to become wetted, as indicated by the suspended drop having a contact angle of less than 90 degrees. This is further discussed in U.S. patent applications Ser. Nos. 10/649,285 and 10/403,159, which are incorporated by reference herein in their entirety. In some cases, additional energy needs to be added to de-wet the surface. Examples of introducing energy to de-wet a surface by heating the surface are presented in U.S. patent application Ser. Nos. 11/227,759 and 11/227,808, which are incorporated by reference herein in their entirety.
Although the wettability of such surfaces can be controlled through the application of a voltage, they require a power source to heat or provide the voltage to the surface. Additionally, if the objective is to dynamically change wettability upon changes in the environment, then an environmental sensor and a means for deciding when to apply the voltage or heat would also have to be provided.